Nitroglycerin (NTG) ointment has been shown to be effective in the treatment of angina pectoris and congestive heart failure. Its duration of action is usually 4 to 6 hours. This study presents data that show that a new slow-release NTG ointment produces hemodynamic improvement over at least 24 hours. Twenty patients with coronary artery disease were tested with serial gated equilibrium radionuclide ventriculography before and at various stages of continuous, once-a-day use of slow-release NTG ointment and 4 days after cessation of therapy. NTG ointment significantly (p less than 0.005) decreased left ventricular end-diastolic and end-systolic volumes both at rest (23% and 33%) and during handgrip exercise (22% and 32%) when examined after continuous usage of at least 24 hours. Ejection fraction increased 21% at rest, from 0.42 +/- 0.15 to 0.51 +/- -0.18, p less than 0.0005). The ratio of peak systolic pressure to end-systolic volume increased 85% at rest (p less than 0.05) and 54% during exercise (p less than 0.01). All values had returned to baseline 4 days after cessation of treatment. Thus, slow-release NTG ointment may be useful in the treatment of angina pectoris and congestive heart failure on a once-a-day basis.